Advantage of Multichannel Decision Feedback Equalizer on Underwater Acoustic Communication

Underwater acoustic digital communication was investigated by simulation under conditions of various distortions which seem to degrade communication performance, such as multipath or Doppler shift. M-sequence data was used as transmission data. The signal band was 20 kHz±4 kHz, and the modulation method was 16-quadrature amplitude modulation (16-QAM). The received data was demodulated using a multichannel decision feedback equalizer (DFE). In this paper, the effect of feedforward tap allocation on communication performance under an intensive multipath condition is considered. It became clear that the communication performance is advanced by utilizing multipaths, that this advantage is distinguished when the signal-to-noise ratio (SNR) of the input signal is small, that it is necessary to consider the trade-off between this advantage and the instability caused by a large number of taps, and that this advantage is available if ever there is Doppler shift or few multipaths.